In a report on piracy in global markets released on Thursday, the U.S. Trade Representative said Alibaba should intensify its efforts to work with companies to eliminate fakes on platforms like Taobao, the company’s massive online bazaar.

“Brand owners continue to report that Alibaba platforms, particularly Taobao, are used to sell large quantities of counterfeit goods,” the report said.

It also said brand owners continued to complain even after Alibaba enacted new measures for getting fakes off its platforms. “Despite these new procedures, USTR is increasingly concerned by rights holders’ reports that Alibaba Group’s enforcement program is too slow, difficult to use, and lacks transparency.”

The agency said it wouldn’t add Alibaba to its list of notorious markets for fakes, “but it encourages the company to enhance cooperation with all stakeholders to address ongoing complaints.”

In a statement, Alibaba said it is committed to fighting counterfeits. “Counterfeiting is an issue all global e-commerce companies face, and we are doing all we can to address and fight it,” it said.

Alibaba is the world’s largest e-commerce company by some measures and a force in China’s massive online market. The company says it had 386 million active buyers on its platforms for the year ended Sept. 30.

Its Taobao platform is home to largely mom-and-pop stores selling everything from guitar straps to yoga mats for cats. Its Tmall platform largely provides sales venues for major brand owners who run their own online stores there.

On Thursday, the U.S. Trade Representative cited Tmall as one of the platforms that brand owners had criticized. Previous reports focused mostly on Taobao.